1. Field of the Invention
The present invention relates to a fuel injection control apparatus for an internal combustion engine, and more particularly, to a fuel injection control apparatus for an internal combustion engine in which an exhaust gas is improved by injecting a fuel in accordance with an actual drawn air amount.
2. Description of the Related Art
FIG. 7 shows a structure of a conventional fuel injection control apparatus for an internal combustion engine, in which an operation of a throttle is controlled in mechanically association with an accelerator.
In FIG. 7, an engine 1 which is the body of the internal combustion engine comprises, e.g., six cylinders. An air cleaner 102 is mounted to an intake port of an intake passage 103 for purifying a drawn air to be supplied to the engine 101.
An accelerator pedal 104 which is operated by a driver is mechanically connected to a throttle valve 106 in the intake passage 103 through a wire wound around an accelerator link 105. With this arrangement, the throttle valve 106 is associatively operated in accordance with an operation of the accelerator pedal 104, thereby adjusting the air amount to be drawn to the engine 101.
A throttle opening sensor 107 detects a position of the throttle valve 106, i.e., a throttle opening degree .theta..
An intake manifold 108 is mounted to a drawing side of the engine 101 for equalizing an amount of air to be drawn to each of the cylinders.
A drawn air amount sensor 109 detects a drawn air amount Q passing through the intake passage 103.
A crank angle sensor 110 is mounted to a crankshaft of the engine 101, and produces a crank angle signal SGT which corresponds to a crank angle reference position of each of the cylinders (#1 to #6). A cylinder identifying sensor 111 is provided to a camshaft of the engine 101, and produces a cylinder identification signal SGC which corresponds to a specific cylinder (e.g., #1 cylinder).
An injector 112 for injecting a fuel is mounted to each of the cylinders of the engine 101.
An igniter 113, an ignition coil 114, a distributor 115 and sparkplugs 116 constitute an igniting apparatus of the engine 101.
The igniter 113 comprises a power transistor for exciting the ignition coil 114. The ignition coil 114 comprises a transformer, and outputs a high voltage signal from a secondary coil by shutting off electricity of a primary coil. The distributor 115 distributes the high voltage signal from the ignition coil 114 to each of the spark plugs 116.
Each of the sparkplugs 116 is provided in a combustion chamber of each of the cylinders. The sparkplug 116 generates an electrical discharge spark by the high voltage signal applied through the distributor 115, thereby burning a mixed gas in each of the cylinders for driving the engine 101.
An exhaust passage 117 discharges, an exhaust gas produced after the mixed air is burnt in the engine 101, into the atmosphere. A catalyst converter 118 is mounted to an exhaust port of the exhaust passage 117 for purifying the exhaust gas.
The throttle opening degree sensor 107, the drawn air amount sensor 109, the crank angle sensor 101 and the cylinder identifying sensor 111 constitute various sensors for detecting the driving state of the engine 101.
Further, as the occasion demands, other various sensors are also provided, such as a revolution number sensor (which will be described later) for detecting the number of revolutions of the engine based on the crank angle signal SGT, a water temperature sensor for detecting a cooling water temperature of the engine 101, and an accelerator pedal opening degree sensor (not shown) for detecting a depressed amount of the accelerator pedal as an opening degree of the accelerator pedal.
A control unit 120 comprising a microcomputer includes a fuel injection (injector) control apparatus and an ignition control apparatus, and calculates an appropriate fuel injection amount and igniting timing of the engine 101 based on detected information (driving state) from the various sensors and outputs a control signal in accordance with control amounts of various parameters.
The injector control apparatus in the control unit 120 calculates an appropriate fuel injection amount based on the drawn air amount Q from the drawn air amount sensor 109 and the crank angle signal SGT (engine revolution number) from the crank angle sensor 110. Then, the injector control apparatus determines which cylinder should be subject to fuel injection, based on the cylinder identification signal SGC from the cylinder identifying sensor 111, and outputs an injection signal J to the injector 112 of the corresponding cylinder to inject a fuel.
Further, the ignition control apparatus in the control unit 120 outputs an ignition signal P to the igniter 113 for exciting the ignition coil 114, and ignites the sparkplug 116 through the distributor 115 for driving the engine 101.
FIG. 8 is a block diagram for showing a functional structure of the control unit 120, and shows a basic structure of the injector control apparatus.
In FIG. 8, drawn air amount detecting means 1 functions as an input I/F concerning the drawn air mount from the drawn air amount sensor 109, and calculates an actual drawn air amount from a signal indicative of the drawn air amount Q.
The crank angle detecting means 2 functions as an input I/F concerning the crank angle signal SGT from the crank angle sensor 110, and detects a crank angle reference position for every cylinder based on the crank angle signal SGT.
An engine revolution number detecting means 3 functions as an input I/F concerning the revolution number sensor, and calculates the engine revolution number Ne based on the crank angle signal SGT (a cycle of the crank angle reference position).
A basic fuel injection amount calculating means 4 calculates a basic fuel injection amount Fo which is necessary for combustion, based on the drawn air amount Q detected by the drawn air amount detecting means 1 and the engine revolution number Ne calculated by the engine revolution number detecting means 3.
A fuel injection amount correcting means 5 detects states of the engine 101 such as an accelerating/decelerating driving state thereof based on sensed information indicative of driving states of the engine 101 including the drawn air amount Q (such as cooling water temperature and load of the engine), and calculates a corrected fuel injection amount Fa which is obtained by correcting the basic fuel injection amount Fo.
When an accelerating driving state is detected based on a variation amount .DELTA. of the drawn air amount Q for example, the fuel injection amount correcting means 5 corrects to increase the basic fuel injection amount Fo to provide a corrected fuel injection amount Fa, so as to compensate a shortage of a fuel for acceleration. Therefore, an excellent fuel injection control is realized even during a transitional driving state such as accelerating or decelerating driving state.
The throttle opening degree detecting means 6 calculates a value of an actual throttle opening degree based on a signal indicative of a throttle opening degree .theta. from the throttle opening degree sensor 107.
A non-synchronous fuel injection amount calculating means 7 determines that the driving state is a rapid accelerating driving state based on a variation amount .DELTA..theta. of the throttle opening degree .theta. detected by the throttle opening degree detecting means 6, and calculates a non-synchronous fuel injection amount Fb for injecting fuel non-synchronously.
A fuel injection control means 8 produces an injection signal J which corresponding to a final fuel injection amount in accordance with the corrected fuel injection amount Fa and the non-synchronous fuel injection amount Fb.
Next, referring to timing charts in FIGS. 9 to 14, an operation of the conventional fuel injection control apparatus for the internal combusiton engine shown in FIGS. 7 and 8.
FIG. 9 shows an operation of the injector 112 of each of the cylinders at the time of normal driving, and shows a relationship between processes (comprising four cycles, i.e., compression, combustion, evacuation and air-drawing) of each of the cylinders (#1 to #6) of the engine 101, and operational timings of the injection signals J1 to J6 with respect to the cylinders (#1 to #6).
In FIG. 9, the cylinder identification signal SGC includes a pulse corresponding to the #1 cylinder only, so as to identify the #1 cylinder.
The crank angle signal SGT comprises a plurality of pulses having edges corresponding to crank angle reference positions of the respective cylinders.
In this case, FIG. 9 shows that a crank angle position in a region from a falling-down edge to a rising edge of the crank angle signal SGT when the cylinder identification signal SGC is H (high) level corresponds to an igniting timing of #1 cylinder.
Each of processes of #1 cylinder to #6 cylinder are synchronized with each of the edges of the crank angle signal SGT.
FIGS. 10 to 11 show an operation of the fuel injection amount correcting means 5, and show a correcting operation to increase a fuel injection amount at the time of acceleration.
In this case, the throttle valve 106 is associatively operated with the depressing operation of the accelerator pedal 104 substantially in a synchronized manner. However, because the actual drawn air amount Q is behind the operation of the throttle valve 106, the actual drawn air amount Q is varied after the accelerator pedal opening degree .alpha. is varied.
When the fuel injection amount correcting means 5 determines that the driving state is an accelerating driving state based on a variation of the drawn air amount Q, a driving time of, e.g., an injection signal J6 with respect to #6 cylinder is elongated to correct a fuel injection amount such as to increase the same, thereby substantially making it possible to supply a fuel in an amount necessary for combustion.
FIGS. 12 to 14 show an operation of the non-synchronous fuel injection amount calculating means 7, and show an injection timing of the non-synchronous fuel injection amount Fb at the time of rapid acceleration.
In FIGS. 12 to 14, when the non-synchronous fuel injection amount calculating means 7 determines that the driving state is a rapid accelerating driving state, the non-synchronous fuel injection amount calculating means 7 produces, apart from driving times t4 to t6 of normal injection signals J4 to J6, injection signals (see the shaded portions) each having a constant pulse width t with respect to, e.g., #4 and #6 cylinders.
Further, in FIG. 13, when the non-synchronous fuel injection amount calculating means 7 determines that the driving state is a rapid accelerating driving state, the non-synchronous fuel injection amount calculating means 7 produces injection signals (see the shaded portions) each having a pulse width t with respect to, e.g., #4 to #6 cylinders.
With this arrangement, it is possible to supply, as a non-synchronous fuel injection amount Fb, a fuel in an amount corresponding to a predetermined pulse width t.
First, at a falling-down time point tn of the crank angle signal SGT, the drawn air amount detecting means 1 detects a drawn air amount Q(n) during falling-down of the crank angle signal SGT, and the engine revolution number detecting means 3 detects the engine revolution number N(n) from a measured cycle T(n) during falling-down of the crank angle signal SGT.
The basic drawn air amount calculating means 4 calculates the basic fuel injection amount Fo based on the drawn air amount Q(n) and the engine revolution number N(n). The fuel injection control means 8 outputs a fuel injection amount as corrected in accordance with a driving state, in a form of injection signals J1 to J6 with respect to the respective injectors 112 as shown in FIG. 9.
The injection signals J1 to J6 are produced such as to start injecting a fuel synchronously with the falling-down of the crank angle signal SCT during an evacuating process of each of the cylinders.
At that time, the fuel injection amount is calculated based on the drawn air amount and the engine revolution number at the time point prior to the air-drawing process of a cylinder to which a fuel is to be injected. However, at the time of normal driving, because there is no large variation in the drawing air amount Q and the engine revolution number Ne, any problem is not caused.
However, at the time of transition driving such as an accelerating or decelerating driving, the drawn air amount Q and the engine revolution number Ne are varied before and during the air-drawing process of a cylinder to which a fuel is to be injected.
More specifically, a fuel injection amount calculated based on the drawn air amount Q and the engine revolution number Ne before the air-drawing process is too small at the time of acceleration, and is too large at the time of deceleration.
Therefore, the fuel injection amount correcting means 5 determines that the driving state is a transition driving state from a variation amount .DELTA.Q of the drawn air amount Q at the falling-down time point of the crank angle signal SGT, and corrects the fuel injection amount at the time of transition driving. For example, the injection signal J is controlled such that if an accelerating driving state is identified, a correction is made to increase the fuel injection amount to compensate the shortage of fuel, and if a decelerating driving is identified, a correction is made to decrease the fuel injection amount to avoid the excessive fuel.
In FIG. 10 for example, the accelerator pedal opening degree .alpha. is increased from a position just before the air-drawing process of #4 cylinder is started. In response to this accelerating driving, the drawn air amount Q is increased from a position corresponding to about one third from the start of the air-drawing process of #4 cylinder.
Meanwhile, in FIG. 11, a depressing timing of the accelerator pedal 104 is a little late as compared with a case shown in FIG. 10, and the accelerator pedal opening degree .alpha. is increased from a position just after the air-drawing process of #4 cylinder is started, and the drawn air amount Q is increased at a position corresponding to about two third from the start of the air-drawing process of #4 cylinder.
In FIGS. 10 and 11, with a falling-down of the crank angle signal SGT which is the fuel injection starting timing with respect to, e.g., #6 cylinder, an acceleration is identified in view of variation in the drawn air amount. Therefore, the injection signal J6 with respect to #6 cylinder is elongated to make a correction to increase the fuel injection amount.
However, because this correction amount is determined by matching under a predetermined condition, an air-fuel ratio varies widely depending upon a depressing timing or a depressing amount of the accelerator pedal, and there is a fear that an exhaust gas is deteriorated. Further, with a falling-down of SGT which is the fuel injection starting timing with respect to #5 cylinder, there is no variation in the drawn air amount Q, and such a timing is the one before the accelerating driving state is identified. Therefore, the fuel is not corrected.
In FIGS. 10 and 11, the fuel injection amount of #5 cylinder is substantially constant, and a fuel is injected in the latter half of the evacuation process. Therefore, the air-fuel ratio of #5 cylinder is determined by an actual air charging amount of #5 cylinder.
However, between the cases shown in FIGS. 10 and 11, depression timings of the accelerator pedal are different and variation timings of the drawn air amount Q are also different. Therefore, air charging amounts of #5 cylinder are different and thus, air-fuel ratios are also different.
As described above, in the conventional apparatus, the throttle opening degree .theta. relies upon the operation of the accelerator pedal, and the air charging amount of the engine 101 is varied for every operation of the accelerator pedal. Therefore, the air-fuel ratio and the exhaust gas vary widely, which brings out a deterioration of the exhaust gas.
Further, at the time of rapid acceleration, even if a correction is made to increase the fuel injection amount for a normal acceleration, a fuel in an amount necessary for combustion (a fuel in an amount which meets an actual charging air amount in a cylinder) is not supplied in time, which brings out an excess or a shortage of fuel. In order to prevent this, a non-synchronous fuel injection is conducted as temporary measures.
More specifically, if the non-synchronous fuel injection amount calculating means 7 determines that the driving state is a rapid accelerating driving state in view of the throttle opening degree .theta. or the like, the non-synchronous fuel injection amount calculating means 7 produces an injection signal (see the shaded portions in FIG. 12) corresponding to the non-synchronous fuel injection amount Fb, irrespective of a fuel injecting timing for every cylinder.
The non-synchronous fuel injection amount calculating means 7 conducts a fuel injection non-synchronously with a falling-down timing of the crank angle signal SGT with respect to a cylinder whose drawn air amount Q is expected or predicted to be increased, thereby compensating an excess or shortage of fuel.
For example, when a variation amount .DELTA..theta. of the throttle opening degree .theta. during a predetermined time period is equal to or greater than a predetermined value, a determination is made that the driving state is a rapid accelerating driving state, and a non-synchronous fuel injection is conducted with respect to a cylinder which is in an evacuating process or air-drawing process when the rapid acceleration is detected.
Therefore, there can be various cases for such a non-synchronous fuel injection depending upon a timing when the rapid acceleration is detected.
For example, FIG. 12 shows a case in which a rapid acceleration is detected at a substantially intermediate position of a interval T1, and a non-synchronous fuel injection is conducted.
If a fuel injection amount by a normal fuel injection (synchronous injection) and a fuel injection amount by non-synchronous injection when a rapid accelerating is detected are added, fuels in amounts corresponding to injector driving times t4+t, t5+t and t6+t by injection signals J4 to J6 are charged to #4 to #6 cylinders, respectively.
FIG. 13 shows a case in which a rapid acceleration is detected at the first half position of the interval T1, and a non-synchronous fuel injection is conducted.
In this case, at a time point when the non-synchronous injection is to be started, because a normal fuel injection (synchronous injection) is conducted for #5 cylinder, a non-synchronous injection is not conducted. Therefore, fuels in amounts corresponding to injector driving times t4+t, t5+t and t6+t by injection signals J4 to J6 are charged to #4 to #6 cylinders, respectively, and a fuel injection amount for #5 cylinder is reduced as compared with the case shown in FIG. 12.
FIG. 14 shows a case in which a rapid acceleration is detected at the latter half position of the interval T1, and a non-synchronous fuel injection is conducted.
In this case, as in the case shown in FIG. 12 in which the rapid acceleration is detected at an intermediate position of the interval T1, non-synchronous injections are conducted with respect to #4 to #6 cylinders and therefore, fuels in amounts corresponding to injector driving times t4+t, t5+t and t6+t by injection signals J4 to J6 are charged to #4 to #6 cylinders.
However, the non-synchronous fuel injecting timing shown in FIG. 14 corresponds to an end of the air-drawing process of #4 cylinder. Together with this fact, a supply of fuel is also retarded and thus, all of non-synchronously injected fuel can not be charged into #4 cylinder during this cycle. Therefore, remaining fuel which was not charged into #4 cylinder is to be charged at a next air-drawing process of #4 cylinder.
As described above, a timing for detecting a rapid acceleration is varied depending upon a charging amount of fuel for a cylinder, even in one fuel injection interval. Therefore, there is a possibility that an amount of fuel increases excessively and the air-fuel ratio is inclined toward a rich side, or an amount of fuel decreased excessively and the air-fuel ratio is inclined toward a lean side.
Further, because a non-synchronous injection control at the time of a rapid acceleration is conducted when a variation amount .DELTA..theta. of a throttle opening degree during the predetermined time period is equal to or greater than the predetermined value, the air-fuel ratio is varied also depending upon a speed or an amount (accelerator pedal opening degree .alpha.) of depression of the accelerator pedal 104.
Furthermore, even if the accelerator pedal is depressed in the same manner, if it is depressed in a different interval, an excess or shortage of fuel is generated because the structure of air-drawing portion of the engine 101 including intake manifold 108 is different and drawing air amounts Q of the cylinders are also different.
There only exists, as a non-synchronous injection at the time of a rapid acceleration, a fuel injection based on assumption in which a constant amount of fuel is injected with respect to a specific cylinder when the rapid acceleration is determined.
Although a correction for increasing a fuel amount at the time of acceleration and a fuel amount by the non-synchronous fuel injection are determined by matching, it is difficult to set the optimum value which meets all of the driving conditions. Therefore, there is a fear that an air-fuel ratio varies depending upon a timing and an amount of depressing the accelerator pedal 104, which may deteriorate the exhaust gas.
Thereupon, there are conceivable control methods such as a method for varying a fuel injection ratio in accordance with a timing of depressing the accelerator pedal, and a method for varying a fuel injection amount in accordance with a speed of depressing the accelerator pedal. However, a huge number of matching data is necessary for determining the optimum fuel amount that meets every timing and amount of depressing the accelerator pedal and a program control logic is complicated, which is impractical.
Although the above description has been made while taking the case of acceleration, even at the time of deceleration, a deviation in the drawn air amount Q is generated as in the case of the acceleration, depending upon a closing timing of the throttle vale 106.
Although there is not shown here in the drawings, there has also been developed a throttle control apparatus which electronically control the operation of the throttle valve 106 in accordance with an accelerator pedal opening degree .alpha. using a throttle actuator having a motor, without using a mechanical transmission apparatus for adjusting a throttle opening degree .theta..
In this case, the throttle valve 106 actually controls in accordance with a target throttle opening degree, after a predetermined time period (delay time) is elapsed after the accelerator pedal 104 is operated. A follow-up speed of the throttle valve 106 is restrained by the maximum driving speed of the motor.
In the fuel injecting timing, it is conceivable to control the fuel injection amount at the current time, in view of a timing in which an injected fuel is actually drawn to the engine 101, and in view of a throttle opening degree after a predetermined delay time is elapsed. However, there has not been proposed to reliably supply a fuel injection amount in accordance with a drawn air amount when the fuel is drawn to the engine 101.
Therefore, it is impossible to accurately calculate an injection signal J in accordance with the drawn air amount by the operation of the throttle valve 106 after the predetermined time period is elapsed in response to the operation of the accelerator pedal 104. Particularly, it is extremely difficult to control the fuel injection amount at the time of transitional driving state in the most suitable manner.
As described above, in the conventional fuel injection control apparatus for an internal combustion engine, it is not impossible to calculate the optimum fuel injection amount in accordance with an actual drawn air amount during a transitional driving state and therefore, there is a problem that an air-fuel ratio is deviated and an exhaust gas is deteriorated.
Further, even if an attempt is made to variably control a fuel injection amount in accordance with a timing or a speed of depressing the accelerator pedal 104, because a huge number of matching data is required, there is a problem that a program control logic is complicated.